The invention relates to a hub construction for a rotatable chair, whereby an uncomplicated and robust plain bearing design is provided.
A large amount of designs have been used for the rotational bearings in the construction of revolving chairs. A typical revolving chair consists of a set structure having a variety of forms, a column-type support under the seat, and a base part, which may be provided with wheels. The column support may comprise a spring or gas suspension structure for providing a suspension effect improving the comfort when sitting.
The rotational movement itself is made possible by providing a torsional bearing in the column. A common solution is a ball or roller bearing for example under the lower end of the column, whereby the bearing is a thrust bearing carrying the total vertical load. There are also a number of designs having a ball bearing surrounding the column.
In a more economical solution, the seat structure rests on a sleeve enclosing a corresponding cylindrical pin. The inner surface of the sleeve and the outer surface of the pin, as well as the lower edge of the sleeve and the corresponding counter surface, form plain bearing surfaces. The outer surface of the sleeve is conical for fitting into a corresponding conical recess in the seat. The common material used for the sleeve is plastic.
In patent GB 1 297 580 there is disclosed a hub construction for a rotatable chair. On a vertical, cylindrical pin attached to the chair's base pedestal is mounted a bushing, the outer surface of which is conical, tapering upwards. This cone fits a corresponding conical recess on the underside of the chair seat, and is provided with a slit in order to compensate for wear and/or tolerances in the facing parts constituting the plain bearing. The conical bushing is made from a durable material, preferably nylon.
In U.S. Pat. No. 6,619,742 there is disclosed a hub construction comprising a plain bearing having conical plastic parts. The upper bearing carries the vertical load and the lower bearing is spring loaded in order to eliminate any play.
In patent FI 104228 there is disclosed a hub construction for a rotatable chair, consisting of a pin enclosed by a plastic sleeve.
These structures comprising plain bearings are of a limited durability due to the properties of the plastic material.